Home and industrial controls are usually powered by a 24V AC system. For traditional power solution for those applications, as shown in FIG. 1, an AC/DC converting apparatus 100 having a diode rectifier bridge 101, a high voltage bulk capacitor 102, and a high voltage DC/DC converter 103 is needed to convert a 24V AC voltage to a desired DC output voltage Vout to power the home and industrial control circuits. As shown in FIGS. 2A and 2B, the diode rectifier bridge 101 is configured to convert positive and negative half cycles of the AC input voltage Vin to a full-wave-rectified voltage waveform with positive polarity. As shown in FIG. 2C, the high voltage bulk capacitor 102 is configured to smooth the full-wave-rectified voltage waveform and to make a DC input voltage Vindc continue nearing a peak voltage Vpeak during low portions of the full-wave-rectified voltage waveform. The high voltage DC/DC converter 103 is used to regulate the DC input voltage Vindc shown in FIG. 2C to the desired DC output voltage Vout.
For a trend of smart home and industrial automation, more power and/or current are needed from the 24V AC system. Current applications can require up to 1 A/30 W. The diode rectifier bridge 101 will be generating a lot of heat in the AC/DC converting apparatus 100. This can cause the system malfunction, like a thermostat cannot read room temperature accurately. In addition, more and more bulk capacitors are needed for higher power, which leads to high system cost and takes too much space of the system.
It would be desirable therefore to provide an AC/DC converting apparatus and method that can eliminate the need of the diode rectifier bridge and also can eliminate the need of high voltage bulk capacitors to acquire low total system cost and high conversion efficiency.